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Abstract
Problem: Groundwater contamination is a concern in rural residential subdivisions where numerous septic systems and private wells are sited in close proximity. Although most state codes regulate the construction and location of private wells, these regulations do not usually account for site-specific conditions that may impact drinking-water quality.
Purpose: Groundwater models provide a technical basis for delineating groundwater flow to domestic wells. Despite their widespread use in the hydrologic sciences, planners and developers rarely have access to such models. We aimed to assess existing regulations for domestic wells and septic systems and illustrate how groundwater models can be used to evaluate strategies for additional drinking-water protection in unsewered residential subdivisions.
Methods: We developed groundwater flow models for two subdivisions in southern Wisconsin, analyzed the results, and disseminated them to local officials, developers, and residents.
Results and conclusions: Models of both subdivisions indicate that deeper individual wells or a single community well within a protected source area would improve the likelihood of obtaining high-quality drinking water. In response, several homeowners in one subdivision chose to pay for deeper wells and well casings or individual home water-treatment systems. The developer of the second site incorporated an unenforceable recommendation for deeper well casings into subdivision covenants, but none of the wells drilled so far have followed the recommendation. Implementing and enforcing well construction or setback criteria based on model results may require changing Wisconsin state codes to explicitly define what can and cannot be regulated at the local level.
Takeaway for practice: Hydrogeologists can use standard groundwater modeling methods and information about local hydrologic conditions to inform planners as they develop guidelines to improve drinking-water quality. Partnerships between local hydrogeologists and planners are essential because differences in hydrogeologic setting, groundwater quality concerns, and regulatory structure will cause model results and proposed guidelines to vary on a case-by-case basis.
Research support: Funding for this research was provided by the EPA Science to Achieve Results (STAR) graduate fellowship program, the University of Wisconsin Groundwater Resources Advisory Council (administered by the Wisconsin Water Resources Institute), and the Wisconsin Department of Natural Resources.
Acknowledgments
This article was improved by discussions with Brian Simmert and Brian Cunningham of the Sauk County Department of Planning and Zoning. We thank Dane County Executive Kathleen Falk, site developer Dennis Midthune, and local homeowners for facilitating the Savannah Valley subdivision study. We also thank the editor and three reviewers for their helpful comments and suggestions.
Notes
a. Based on well completion in a confined or unconfined aquifer.
b. Based on well seal (isolated from the surface).
c. Based on soil type and infiltration rate.
d. Based on aquifer depth.
e. Based on well depth and topography (elevation of well relative to septic system).
f. Based on topography (elevation of well relative to septic system).
1. The Wisconsin administrative code also requires that well casings extend at least 30 feet (9.1 meters) below ground surface into sandstone, 40 feet (12.2 meters) into other bedrock types, and at least 25 feet (7.6 meters) below ground and 10 feet (3 meters) below the water table in unlithified surficial aquifers (Well construction and pump installation, 2006).
2. Preferential flow paths (faults, fractures, or other highly permeable rocks or sediments) allow contaminants to travel relatively quickly through an aquifer and may limit the opportunity for contaminant dilution or degradation. Domestic wells that intersect these flow paths may be susceptible to contamination from sources located much further away than would otherwise be expected. Hydrogeologists with a good knowledge of local conditions should have a feel for the types of features that may be present and be able to account for them in their groundwater models.
